[Omake] allowing for lazy extends?

[Aleksey Nogin]

On 28.01.2007 16:04, Erick Tryzelaar wrote:

> Aleksey Nogin wrote:
>>> Without it, I run into all sorts of issues because "extends" forces 
>>> evaluation, even if it's a lazy variable. So I have to do all sorts 
>>> of hacks in order to avoid extending things until the last possible 
>>> moment.
>>
>> Note that you can implement lazy extension yourself:
> 
> Thanks for that! That does exactly what I want. I did notice that it 
> does add some extra things (name, var, val) to my object, which I'm not 
> sure is on purpose:

No - this was a combination of two unfortunate things:

1. In 0.9.8, the function arguments are scoped the exact same way as 
object fields, so it is very easy to accidentally get function arguments 
"spilled" into an object. This is something that 0.9.9 is supposed to 
address, but for the time being it is very annoying.

2. I tried to address "1" by making keeping the "vars" variable and only 
exporting the correct fields, but did not do it correctly - the vars was 
always empty and "export $(EMPTY)" actually exports everything, not 
nothing (I've filed http://bugzilla.metaprl.org/show_bug.cgi?id=636 ). 
The correct form is:

lazy_extend(name) =
    private.Obj = $(getvar $(name))
    public.vars[] =
    private.skip[] =
       $'$class'
       object-length
       object-mem
       object-add
       object-find
       object-map
       object-foreach

    lazy_update(var, val) =
       if $(not $(mem $(var), $(private.skip)))
          public.vars[] += $(var)
          this = $(obj-add $(this), $(var), $`(obj-find $(getvar 
$,(name)), $,(var)))
          export vars $(public.vars)
       export vars $(public.vars)

    obj-map($(private.Obj), $(lazy_update))

    export $(public.vars)


Aleksey